OpenMW-CS height edit (PR) should now handle edges of the world properly. Here's a smiley and a new landmass I drew as a test.https://imgur.com/a/I2nIrzJ

I've tested this quite thoroughly, and while there are some special cases where you can break some land, in most cases it should be reliable. I've found one way to break it: Making extreme land height changes at the cell edges bordering missing lands. The whole process would be something like this: Make a new cell and land in middle of nowhere (e.g. 50,50), then make a square of 9x9 cells, and selectively pick the middle vertexes at cell edges, drag them really low of really high, delete some of the cells and the lands, and then try to paint the deleted lands back. There will be extreme changes at the cell edge, and it's likely that the automatic land creation and limiting function is unable to solve the problem. This results in land records that can't be saved safely without data corruption because of extreme height differences. Fixing such problem requires deleting the land records an rebuilding them from scratch (or pressing undo button). It's possible to code workarounds and improve the automatic land limiting function, but for such extereme cases I'd prefer having better manual control (e.g. option to turn automatic land limiting off in order to fix it manually).

More testing is of course of use, land editing is a fairly big feature, so there are many places that can go wrong. This was seen already at texture editing, as one quite severe bug got to 0.45 after all without anyone noticing (this is fixed at git, so it's resolved already for 0.46 though). Other than just asking for more testing, I feel like the base feature (editing terrain heightmaps or "terrain shape edit") is more than just bare-bones -ready.